Question: Christopher is 4 times as old as Tiffany and is also 12 years older than Tiffany. How old is Christopher?
Solution: We can use the given information to write down two equations that describe the ages of Christopher and Tiffany. Let Christopher's current age be $c$ and Tiffany's current age be $t$ $c = 4t$ $c = t + 12$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $c$ is to solve the second equation for $t$ and substitute that value into the first equation. Solving our second equation for $t$ , we get: $t = c - 12$ . Substituting this into our first equation, we get the equation: $c = 4$ $(c - 12)$ which combines the information about $c$ from both of our original equations. Simplifying the right side of this equation, we get: $c = 4c - 48$ Solving for $c$ , we get: $3 c = 48$ $c = 16$.